OST-HER2 (AOST-2121)

September 8, 2026: OS Therapies (NYSE: OSTX) reported an interim 3-year overall survival analysis from its Phase 2b OST-HER2 trial in fully resected, pulmonary metastatic osteosarcoma. The 3-year OS rate was 71.2% for OST-HER2-treated patients versus 45.8% for a comparable combined published historical control (p=0.002). The analysis included 41 enrolled patients; two patients have not yet reached the 3-year timepoint, with visits scheduled for September 2026 and early October 2026, and six patients were lost to follow-up.

The company said it expects to complete final data analysis in the next month and is in ongoing regulatory discussions. It plans regulatory submissions for OST-HER2 to FDA, MHRA, EMA, and Australia’s TGA in the coming months, targeting a BLA in the U.S. under Accelerated Approval and conditional marketing applications in the U.K., Europe, and Australia in Q4 2026, with potential commercial availability in 2027. A mid-September 2026 FDA Type C Statistical Methods Meeting is upcoming, after which the company intends to request rolling review of the BLA.

Separately, OS Therapies received $3.15 million in VAT refunds and said an additional $7.2 million in refundable VAT and R&D tax credits is pending; these funds are earmarked for starting the confirmatory Phase 3 trial in the U.K.